* Opposition wants full recount vote, government refuses
* Violence overshadows Capriles' surprisingly strong showing
* Maduro set to be sworn in as president on Friday
Henrique Capriles may have cemented his status as Venezuela's undisputed opposition leader, but he faces an uphill battle in his challenge to election results that narrowly handed the OPEC nation's presidency to Nicolas Maduro.
The youthful state governor won a surprising 49 percent of ballots in the snap election called to succeed late socialist leader Hugo Chavez, who comfortably beat Capriles in October before succumbing to cancer.
Capriles refused to recognize Maduro's narrow victory and called supporters into the streets for peaceful protests to back his demands for a full manual recount.
But some of those demonstrations turned violent and at least eight people were killed. The government immediately blamed Capriles and accused him of trying to trigger a coup.
The violence overshadowed Capriles' biggest achievement to date - pulling over half a million Chavez supporters into the opposition in a short campaign despite Maduro's ample use of state resources - and forced him to scrap the tactic of street demonstrations.
Furthermore, he has so far publicly presented little in the way of smoking-gun evidence to show the vote was stolen, though his campaign alleges more than 3,000 irregularities from armed thugs in polling stations to mismatches on tally sheets.
"Unless it can be demonstrated soon that Maduro committed massive fraud ... it will be difficult for the opposition to make the case that the current government stole the election," said Carl Meacham, director of the Americas Program at the Center for Strategic and International Studies.
Athletic and wiry with a reputation for drawing crowds of women, Capriles has rejuvenated the image of an opposition that was for years dominated by discredited old-guard politicians.
He also helped redirect the opposition's ineffective ideological attacks on Chavez into sharper criticism about bread-and-butter issues such as crime, inflation and blackouts.
Capriles, governor of Miranda state, had promised during the campaign to keep the best of Chavez's social welfare programs while scrapping socialist economic policies for a Brazil-style system that respects free enterprise while helping the poor.
Sunday's vote put him firmly at the helm of the disparate opposition coalition, in contrast to Maduro's weak mandate and limited control over his own similarly unruly coalition of socialists that for years were held together largely by Chavez's magnetic charisma.
Capriles denies any link to this week's violence and has called on supporters to use peaceful protests, like banging pots and pans every night, while insisting on a recount.
"We want the country to resolve this political crisis, but to do so it needs to count the votes one by one," Capriles said.
Though the violence put him on the back foot, opposition media are now questioning exactly what happened. They say officials may have exaggerated attacks on government-run clinics and blamed Capriles supporters for some deaths that they were not responsible for.
Capriles' refusal to recognize Maduro as president seems increasingly futile as electoral authorities prepare to swear in the 50-year-old former bus driver and Chavez protege on Friday in the presence of heads of state from around Latin America.
"The electoral system worked absolutely perfectly," said National Electoral Council (CNE) head Tibisay Lucena, whom the opposition accuse of being in the ruling party's pocket.
Meanwhile, foreign governments ranging from Latin American states to Russia and China have recognized the results. The United States - which was at odds with Chavez for most of his tenure - and the European Union have so far stayed on the fence.
Refusing to acknowledge Maduro's legitimacy is a risky strategy. Maduro has responded by threatening not to recognize Capriles as governor of Miranda, potentially cutting off funding for the populous state that includes parts of Caracas.
The head of Congress has said he will not let opposition lawmakers speak during debates unless they accept Maduro.
Capriles has not alleged fraud in the way the opposition did after Chavez won a 2004 recall referendum. Rather, he has presented a list of voting day misdeeds he insists demonstrate the need for a complete recount, instead of the partial audit already carried out by electoral authorities.
He says opposition witnesses responsible for ensuring a clean vote were forced out of 286 voting centers, in some cases at gunpoint, potentially affecting some 723,000 votes.
Ruling Socialist Party activists illegally campaigned for Maduro next to 421 polling centers, Capriles charged.
He also alleged 564 centers saw cases of "assisted voting" in which Maduro sympathizers stood at machines and instructed voters how to cast their ballot - also a violation of the rules.
One Venezuelan observation group said its quick count showed a technical tie, and that it could not determine the winner because it did not have enough data to do a complete count.
The official results gave Maduro 50.8 percent support.
Capriles, whose camp is convinced he received more votes than the official tally reflects, insists he has no choice but to demand a recount.
"If I see these irregularities, what do I do? What do I tell the country? What was the actual result?" Capriles said.
His team on Wednesday filed paperwork with the election board disputing the result. The ruling Socialist Party said it would publish the vote counts from each polling center on Wednesday, but as of Thursday there was no sign it had done so.
Party representatives did not answer calls seeking comment.
Capriles noted that in some cases after previous elections the CNE has annulled results from some voting centers due to irregularities and ordered that some ballots be cast again.
Despite initially saying he was open to a complete recount, Maduro is now opposing it and accusing the opposition of trying to destabilize Venezuela with its protests.
One well-known opposition blogger, Francisco Toro, said Capriles needs to prove he won the vote rather than suggesting he would have won if there hadn't been irregularities.
"So far that evidence has been forthcoming only in tiny fragments, fragments that seem tangential," Toro wrote. "In the two places that matter right now - the international community and the armed forces - a fraud claim conjugated in the conditional is just not going to cut it."